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cos(t)<1/5 inequation

A inequation with variable

The solution

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cos(t) < 1/5
$$\cos{\left(t \right)} < \frac{1}{5}$$
cos(t) < 1/5
Detail solution
Given the inequality:
$$\cos{\left(t \right)} < \frac{1}{5}$$
To solve this inequality, we must first solve the corresponding equation:
$$\cos{\left(t \right)} = \frac{1}{5}$$
Solve:
Given the equation
$$\cos{\left(t \right)} = \frac{1}{5}$$
transform
$$\cos{\left(t \right)} - \frac{1}{5} = 0$$
$$\cos{\left(t \right)} - \frac{1}{5} = 0$$
Do replacement
$$w = \cos{\left(t \right)}$$
Move free summands (without w)
from left part to right part, we given:
$$w = \frac{1}{5}$$
We get the answer: w = 1/5
do backward replacement
$$\cos{\left(t \right)} = w$$
substitute w:
$$x_{1} = 32.7853649419025$$
$$x_{2} = -11.1969322083546$$
$$x_{3} = 7.65262371318415$$
$$x_{4} = -13.9358090203637$$
$$x_{5} = -95.6172180136984$$
$$x_{6} = 92.8783412016892$$
$$x_{7} = -57.9181061706208$$
$$x_{8} = 45.3517355562617$$
$$x_{9} = -89.3340327065188$$
$$x_{10} = 57.9181061706208$$
$$x_{11} = 83.0508473993392$$
$$x_{12} = 39.0685502490821$$
$$x_{13} = -32.7853649419025$$
$$x_{14} = 13.9358090203637$$
$$x_{15} = -86.5951558945096$$
$$x_{16} = 80.3119705873301$$
$$x_{17} = 1.36943840600457$$
$$x_{18} = 64.2012914778004$$
$$x_{19} = 61.4624146657913$$
$$x_{20} = -17.4801175155342$$
$$x_{21} = -83.0508473993392$$
$$x_{22} = 55.1792293586117$$
$$x_{23} = 89.3340327065188$$
$$x_{24} = 48.8960440514321$$
$$x_{25} = 23.7633028227138$$
$$x_{26} = -36.329673437073$$
$$x_{27} = 17.4801175155342$$
$$x_{28} = -48.8960440514321$$
$$x_{29} = -4.91374690117502$$
$$x_{30} = 76.7676620921596$$
$$x_{31} = -99.1615265088688$$
$$x_{32} = -45.3517355562617$$
$$x_{33} = 36.329673437073$$
$$x_{34} = -23.7633028227138$$
$$x_{35} = 95.6172180136984$$
$$x_{36} = 99.1615265088688$$
$$x_{37} = -55.1792293586117$$
$$x_{38} = 67.7455999729709$$
$$x_{39} = 20.2189943275433$$
$$x_{40} = -26.5021796347229$$
$$x_{41} = -64.2012914778004$$
$$x_{42} = -80.3119705873301$$
$$x_{43} = 74.0287852801505$$
$$x_{44} = 86.5951558945096$$
$$x_{45} = 4.91374690117502$$
$$x_{46} = -70.48447678498$$
$$x_{47} = -51.6349208634413$$
$$x_{48} = 30.0464881298934$$
$$x_{49} = -30.0464881298934$$
$$x_{50} = -76.7676620921596$$
$$x_{51} = 70.48447678498$$
$$x_{52} = -92.8783412016892$$
$$x_{53} = -39.0685502490821$$
$$x_{54} = 834.29420744888$$
$$x_{55} = -654.820710352682$$
$$x_{56} = 11.1969322083546$$
$$x_{57} = -42.6128587442525$$
$$x_{58} = -20.2189943275433$$
$$x_{59} = 51.6349208634413$$
$$x_{60} = 108.183588628058$$
$$x_{61} = -67.7455999729709$$
$$x_{62} = -61.4624146657913$$
$$x_{63} = 42.6128587442525$$
$$x_{64} = -7.65262371318415$$
$$x_{65} = -1.36943840600457$$
$$x_{66} = -74.0287852801505$$
$$x_{67} = 26.5021796347229$$
$$x_{1} = 32.7853649419025$$
$$x_{2} = -11.1969322083546$$
$$x_{3} = 7.65262371318415$$
$$x_{4} = -13.9358090203637$$
$$x_{5} = -95.6172180136984$$
$$x_{6} = 92.8783412016892$$
$$x_{7} = -57.9181061706208$$
$$x_{8} = 45.3517355562617$$
$$x_{9} = -89.3340327065188$$
$$x_{10} = 57.9181061706208$$
$$x_{11} = 83.0508473993392$$
$$x_{12} = 39.0685502490821$$
$$x_{13} = -32.7853649419025$$
$$x_{14} = 13.9358090203637$$
$$x_{15} = -86.5951558945096$$
$$x_{16} = 80.3119705873301$$
$$x_{17} = 1.36943840600457$$
$$x_{18} = 64.2012914778004$$
$$x_{19} = 61.4624146657913$$
$$x_{20} = -17.4801175155342$$
$$x_{21} = -83.0508473993392$$
$$x_{22} = 55.1792293586117$$
$$x_{23} = 89.3340327065188$$
$$x_{24} = 48.8960440514321$$
$$x_{25} = 23.7633028227138$$
$$x_{26} = -36.329673437073$$
$$x_{27} = 17.4801175155342$$
$$x_{28} = -48.8960440514321$$
$$x_{29} = -4.91374690117502$$
$$x_{30} = 76.7676620921596$$
$$x_{31} = -99.1615265088688$$
$$x_{32} = -45.3517355562617$$
$$x_{33} = 36.329673437073$$
$$x_{34} = -23.7633028227138$$
$$x_{35} = 95.6172180136984$$
$$x_{36} = 99.1615265088688$$
$$x_{37} = -55.1792293586117$$
$$x_{38} = 67.7455999729709$$
$$x_{39} = 20.2189943275433$$
$$x_{40} = -26.5021796347229$$
$$x_{41} = -64.2012914778004$$
$$x_{42} = -80.3119705873301$$
$$x_{43} = 74.0287852801505$$
$$x_{44} = 86.5951558945096$$
$$x_{45} = 4.91374690117502$$
$$x_{46} = -70.48447678498$$
$$x_{47} = -51.6349208634413$$
$$x_{48} = 30.0464881298934$$
$$x_{49} = -30.0464881298934$$
$$x_{50} = -76.7676620921596$$
$$x_{51} = 70.48447678498$$
$$x_{52} = -92.8783412016892$$
$$x_{53} = -39.0685502490821$$
$$x_{54} = 834.29420744888$$
$$x_{55} = -654.820710352682$$
$$x_{56} = 11.1969322083546$$
$$x_{57} = -42.6128587442525$$
$$x_{58} = -20.2189943275433$$
$$x_{59} = 51.6349208634413$$
$$x_{60} = 108.183588628058$$
$$x_{61} = -67.7455999729709$$
$$x_{62} = -61.4624146657913$$
$$x_{63} = 42.6128587442525$$
$$x_{64} = -7.65262371318415$$
$$x_{65} = -1.36943840600457$$
$$x_{66} = -74.0287852801505$$
$$x_{67} = 26.5021796347229$$
This roots
$$x_{55} = -654.820710352682$$
$$x_{31} = -99.1615265088688$$
$$x_{5} = -95.6172180136984$$
$$x_{52} = -92.8783412016892$$
$$x_{9} = -89.3340327065188$$
$$x_{15} = -86.5951558945096$$
$$x_{21} = -83.0508473993392$$
$$x_{42} = -80.3119705873301$$
$$x_{50} = -76.7676620921596$$
$$x_{66} = -74.0287852801505$$
$$x_{46} = -70.48447678498$$
$$x_{61} = -67.7455999729709$$
$$x_{41} = -64.2012914778004$$
$$x_{62} = -61.4624146657913$$
$$x_{7} = -57.9181061706208$$
$$x_{37} = -55.1792293586117$$
$$x_{47} = -51.6349208634413$$
$$x_{28} = -48.8960440514321$$
$$x_{32} = -45.3517355562617$$
$$x_{57} = -42.6128587442525$$
$$x_{53} = -39.0685502490821$$
$$x_{26} = -36.329673437073$$
$$x_{13} = -32.7853649419025$$
$$x_{49} = -30.0464881298934$$
$$x_{40} = -26.5021796347229$$
$$x_{34} = -23.7633028227138$$
$$x_{58} = -20.2189943275433$$
$$x_{20} = -17.4801175155342$$
$$x_{4} = -13.9358090203637$$
$$x_{2} = -11.1969322083546$$
$$x_{64} = -7.65262371318415$$
$$x_{29} = -4.91374690117502$$
$$x_{65} = -1.36943840600457$$
$$x_{17} = 1.36943840600457$$
$$x_{45} = 4.91374690117502$$
$$x_{3} = 7.65262371318415$$
$$x_{56} = 11.1969322083546$$
$$x_{14} = 13.9358090203637$$
$$x_{27} = 17.4801175155342$$
$$x_{39} = 20.2189943275433$$
$$x_{25} = 23.7633028227138$$
$$x_{67} = 26.5021796347229$$
$$x_{48} = 30.0464881298934$$
$$x_{1} = 32.7853649419025$$
$$x_{33} = 36.329673437073$$
$$x_{12} = 39.0685502490821$$
$$x_{63} = 42.6128587442525$$
$$x_{8} = 45.3517355562617$$
$$x_{24} = 48.8960440514321$$
$$x_{59} = 51.6349208634413$$
$$x_{22} = 55.1792293586117$$
$$x_{10} = 57.9181061706208$$
$$x_{19} = 61.4624146657913$$
$$x_{18} = 64.2012914778004$$
$$x_{38} = 67.7455999729709$$
$$x_{51} = 70.48447678498$$
$$x_{43} = 74.0287852801505$$
$$x_{30} = 76.7676620921596$$
$$x_{16} = 80.3119705873301$$
$$x_{11} = 83.0508473993392$$
$$x_{44} = 86.5951558945096$$
$$x_{23} = 89.3340327065188$$
$$x_{6} = 92.8783412016892$$
$$x_{35} = 95.6172180136984$$
$$x_{36} = 99.1615265088688$$
$$x_{60} = 108.183588628058$$
$$x_{54} = 834.29420744888$$
is the points with change the sign of the inequality expression.
First define with the sign to the leftmost point:
$$x_{0} < x_{55}$$
For example, let's take the point
$$x_{0} = x_{55} - \frac{1}{10}$$
=
$$-654.820710352682 + - \frac{1}{10}$$
=
$$-654.920710352682$$
substitute to the expression
$$\cos{\left(t \right)} < \frac{1}{5}$$
$$\cos{\left(t \right)} < \frac{1}{5}$$
cos(t) < 1/5

Then
$$x < -654.820710352682$$
no execute
one of the solutions of our inequality is:
$$x > -654.820710352682 \wedge x < -99.1615265088688$$
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       x55      x31      x5      x52      x9      x15      x21      x42      x50      x66      x46      x61      x41      x62      x7      x37      x47      x28      x32      x57      x53      x26      x13      x49      x40      x34      x58      x20      x4      x2      x64      x29      x65      x17      x45      x3      x56      x14      x27      x39      x25      x67      x48      x1      x33      x12      x63      x8      x24      x59      x22      x10      x19      x18      x38      x51      x43      x30      x16      x11      x44      x23      x6      x35      x36      x60      x54

Other solutions will get with the changeover to the next point
etc.
The answer:
$$x > -654.820710352682 \wedge x < -99.1615265088688$$
$$x > -95.6172180136984 \wedge x < -92.8783412016892$$
$$x > -89.3340327065188 \wedge x < -86.5951558945096$$
$$x > -83.0508473993392 \wedge x < -80.3119705873301$$
$$x > -76.7676620921596 \wedge x < -74.0287852801505$$
$$x > -70.48447678498 \wedge x < -67.7455999729709$$
$$x > -64.2012914778004 \wedge x < -61.4624146657913$$
$$x > -57.9181061706208 \wedge x < -55.1792293586117$$
$$x > -51.6349208634413 \wedge x < -48.8960440514321$$
$$x > -45.3517355562617 \wedge x < -42.6128587442525$$
$$x > -39.0685502490821 \wedge x < -36.329673437073$$
$$x > -32.7853649419025 \wedge x < -30.0464881298934$$
$$x > -26.5021796347229 \wedge x < -23.7633028227138$$
$$x > -20.2189943275433 \wedge x < -17.4801175155342$$
$$x > -13.9358090203637 \wedge x < -11.1969322083546$$
$$x > -7.65262371318415 \wedge x < -4.91374690117502$$
$$x > -1.36943840600457 \wedge x < 1.36943840600457$$
$$x > 4.91374690117502 \wedge x < 7.65262371318415$$
$$x > 11.1969322083546 \wedge x < 13.9358090203637$$
$$x > 17.4801175155342 \wedge x < 20.2189943275433$$
$$x > 23.7633028227138 \wedge x < 26.5021796347229$$
$$x > 30.0464881298934 \wedge x < 32.7853649419025$$
$$x > 36.329673437073 \wedge x < 39.0685502490821$$
$$x > 42.6128587442525 \wedge x < 45.3517355562617$$
$$x > 48.8960440514321 \wedge x < 51.6349208634413$$
$$x > 55.1792293586117 \wedge x < 57.9181061706208$$
$$x > 61.4624146657913 \wedge x < 64.2012914778004$$
$$x > 67.7455999729709 \wedge x < 70.48447678498$$
$$x > 74.0287852801505 \wedge x < 76.7676620921596$$
$$x > 80.3119705873301 \wedge x < 83.0508473993392$$
$$x > 86.5951558945096 \wedge x < 89.3340327065188$$
$$x > 92.8783412016892 \wedge x < 95.6172180136984$$
$$x > 99.1615265088688 \wedge x < 108.183588628058$$
$$x > 834.29420744888$$
Rapid solution [src]
   /          /    ___\             /    ___\    \
And\t < - atan\2*\/ 6 / + 2*pi, atan\2*\/ 6 / < t/
$$t < - \operatorname{atan}{\left(2 \sqrt{6} \right)} + 2 \pi \wedge \operatorname{atan}{\left(2 \sqrt{6} \right)} < t$$
(atan(2*sqrt(6)) < t)∧(t < -atan(2*sqrt(6)) + 2*pi)
Rapid solution 2 [src]
     /    ___\        /    ___\        
(atan\2*\/ 6 /, - atan\2*\/ 6 / + 2*pi)
$$x\ in\ \left(\operatorname{atan}{\left(2 \sqrt{6} \right)}, - \operatorname{atan}{\left(2 \sqrt{6} \right)} + 2 \pi\right)$$
x in Interval.open(atan(2*sqrt(6)), -atan(2*sqrt(6)) + 2*pi)